dts: socfpga: Add DTS entry for adding the stmmac glue layer for stmmac.

This patch adds the dts bindings documenation for the Altera SOCFPGA glue
layer for the Synopsys STMMAC ethernet driver.

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/arch/arm/boot/dts/socfpga.dtsi b/arch/arm/boot/dts/socfpga.dtsi
index 537f1a5..ba51d69 100644
--- a/arch/arm/boot/dts/socfpga.dtsi
+++ b/arch/arm/boot/dts/socfpga.dtsi
@@ -443,6 +443,7 @@
 
 		gmac0: ethernet@ff700000 {
 			compatible = "altr,socfpga-stmmac", "snps,dwmac-3.70a", "snps,dwmac";
+			altr,sysmgr-syscon = <&sysmgr 0x60 0>;
 			reg = <0xff700000 0x2000>;
 			interrupts = <0 115 4>;
 			interrupt-names = "macirq";
@@ -454,6 +455,7 @@
 
 		gmac1: ethernet@ff702000 {
 			compatible = "altr,socfpga-stmmac", "snps,dwmac-3.70a", "snps,dwmac";
+			altr,sysmgr-syscon = <&sysmgr 0x60 2>;
 			reg = <0xff702000 0x2000>;
 			interrupts = <0 120 4>;
 			interrupt-names = "macirq";